It is known to provide a motor vehicle with an engine stop-start system for automatically stopping and starting the engine whenever it is determined from driver actions that there is an opportunity to do so in order to reduce fuel consumption and reduce emissions from the engine. However, the inventors herein have recognized potential issues with such systems. In one example, an engine stop-start system that, if the time taken to restart the engine is excessive, may have a restart delay that may lead to dissatisfaction in a user of the motor vehicle. In addition such an excessive delay may also result in actual use problems if the driver wrongly concludes that the system has failed to restart the engine in response to their actions.
Specifically, engine stop-start systems rely on pinion engagement into the ring gear to deliver cranking torque to restart the engine. However, pinion engagement is prohibited if the engine is running because it results in severe damage to the pinion or the ring gear. To avoid damage, the pinion can only be safely engaged at an engine speed of typically 200 RPM or less. When an engine shut down is commanded by the driver this action cannot be reversed until the engine speed has fallen below the safe threshold. This time delay is defined by the rate of engine speed reduction and is extremely critical for customer satisfaction especially when there is a “change of mind scenario.”
In one example, the issues described above may be addressed by a method for controlling an engine drive belt tensioner system of a motor vehicle, comprising controlling the drive belt tensioner system to increase the tension in an associated drive belt to a high belt tension while the engine is being stopped. The motor vehicle may have a stop-start system to automatically stop and start the engine in response to predefined driver actions and the method may comprise using the drive belt tensioner system to increase the tension in the drive belt towards the high belt tension when the actions of the driver indicate that the engine is to be stopped. The engine may be started by a starter motor driveably engageable with a ring gear fastened to a flywheel of the engine and the method may further comprise reducing the tension in the drive belt to a low belt tension to assist with engine starting.
In another example, an engine drive belt tensioner system comprises an actuator to vary the tension in an associated drive belt and a belt tension controller and the belt tension controller is operable to control the actuator so as to increase the tension in an associated drive belt to a high belt tension while the engine is being stopped. The motor vehicle may have a stop-start system to automatically stop and start the engine in response to predefined driver actions and the belt tension controller may be operable to control the actuator to increase the tension in the drive belt towards the high belt tension when the actions of the driver indicate that the engine is to be stopped by the stop-start system. As such, the belt tension controller may be operable to control the actuator to reduce the tension in the drive belt towards the low belt tension limit when the actions of the driver indicate that the engine is to be started.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.